Fluoro-butadiene polymers



Patented Feb. 25, 1947 7 Leroy Frank Salisbury, Wilmington, Del., assignor to E L du Pont de Nemours 85 Company, Wilmington, Del.,a corporation of Delaware No Drawing. Application May 27, 1944, Serial No. 537,727

This invention relates to the preparation of an improved synthetic rubber-like material, and more particularly to synthetic rubber-like material produced by polymerizing a mixture of fluoroprene (2-fiuoro-1,3-butadiene) and styrene, which material is of particular value in electric'alinsulations.

It is well known that the polychloroprene'vul- 3 Claims. (01. 260-865)- canizates have excellent oil'resistance as well as outstanding resistance to sunlight and ozone aging, and have therefore been found to be of value as the outer coatin for electrical insulations. a dielectric as natural rubber, and therefore it has generally been employedasanouter coating over rubber insulations. Polychloroprene, furthermore, does 'not have as good flexibility at: very low temperatures as may be desired for many purposes, so that continual attempts are being made to produce a synth etic elastomer which will exhibit still further improvements in freeze resistance, electrical insulation properties, etc. It has been found that polyfiuoroprene has good oil, sunlight and ozone resistance and shows electrical resistivity and low temperature properties approaching those of natural rubber, but without being modified in some way-it possesses poor procv essing characteristics and inferior tensile properties. i

It is therefore the object of this invention to provide a new synthetic rubber-like material which will have good resistance to sunlight, ozone and oil, and which willpossess good tensile strength and good electrical insulation properties, and which will have materially improved processing properties over those" found in polyfluoroprene itself. I

I have found that a novel series of elastomers, which combine good-flexibility at low tempera! tures and high resistance to deterioration by oil, sunlight and ozone and which exhibit excellent electrical insulation properties, can be produced Polychloroprene, however, is notas good.

the peroxide type (including persulfates), In most cases it is desirable to include a sulfur containing modifying agent. The emulsion of monomers so obtained is polymerized at a temperature usually in the range to 40 C. The resulting latex, after being stabilized with an antioxidant such as phenyl-alpha-naphthylamine, is coagulated, and the rubber-like coagulum is masticated and washed free of residual salts on a corrugated .rubber mill and is finally dried by milling on a. smooth roll. The plastic product is then compounded, molded, and vulcanized. If desiredfor certain'operations, the latex can be compounded and used as such, following conventionalprocedures for the production of articles from rubber latex; i

, It is preferably to use fluoroprene which is sub-Q stantially free of monovinylacetylene and peroxides. It may bepreparedby the vapor phase reaction of monovinylacetylene with hydrogen fluoride, as described in'copending applications of Coffman 8; Salisbury Serial No. 508,241, Coffman 8: Salisbury Serial N 0. 508,242 and SalisburySerial by polymerization to rubber-like products of a monomer mixture comprising 60% to 90%;of fluoroprene and 40%- to 10% of styrene. These products are further characterized by having improved processing characteri'stics and superior tensile strength, as compared with polyfluoroprene itself. That the polymerization of styrene with fiuoroprenev effects a desired, improvement in tensile properties is surprising, since corresponding chloroprene styrene copolymers show no appreciable advantage in this respect. These new, elastomers are preferably produced by the emulsion-polymerization process which, in general, may be carried out as follows.

A mixture containing 60% to 90% of fluoroprene and 40%to 10% of styrene'is dispersed in an aqueous emulsion containing an emulsifying agent anda polymerization catalyst, preferably of No. 508,243, all filed on October 29, 1943. l Emm e p f A mixture of 90 parts of fluoroprene and 10 parts of styrene is emulsified in 157 parts ofan aqueous solution containing 4 parts of sodium oleate, 0!: part of excess sodium hydroxide. 1 part of a formaldehyde/sodium naphthalenesulfonate condensation product, 1 part of'p-otassium persulfate, and 0.1 art of potassium-ferricyanide.

Three-tenths part of lauryl mercaptan is added and the. emulsion is heated for 5.5 hours at v30" C. in a sealedglass-llned vessel equipped for ellicient agitation. 'The resulting latex is treated with an. antioxidant consisting of 2 parts of a phenyl-alpha-naphthylamin and diphenylamine (55:45) mixture dispersed in water; Thestabilizedlatx is coagulated by means of brine, and

acetic acid, masticated and washed on ,a corrugated rubber mill to free it of residual salts and finally dried on a smooth mill atan elevated temperature. The product consists of 93 parts: of coherent, plastic material having better processing characteristics than. polyfiuoroprene; 1 similarly prepared. l C p v The dry polymer is then compounded according to the following formula? I Parts Polymer s ;.,100 Channel carbon black 40 Extra light calcinedmagnesia '10 Sulfur 2 The compounded stock is pressed to the desired shape in a mold and cured for minutes at 153 C. under pressure. The vulcanizate, has a tensile strength of 3320 f lbs./sq..in. at 425% elongation and a 300% modulus of 1730 lbs/sq. in. The

'' s r-A freeze resistance of this ,vulcanizate is excellent,

as indicated by afTi value "of 42 C., and the 1 .oil resistance is quite good, asindicated by a vol- 4 a I those of natural rubber and markedly superior to those of polychloroprene. In further comparison with natural rubber, fluoroprene/styrene copolyume increase of on1y100% after two days in kero- 5 sene at100- C. Furthermore, thevulcanizateisl; characterized by good resilience (S chopper. ret bound of 48%) and much betterozone and sun-] light resistance than natural rubber.

The T value, indicative of freeze resistance, is

determined as follows: A vulcanizateof'uniformf cross-section is str'etched 170% and cooled slow- '3 1y to "70' 05m this stretched condition: The

l I tension on thesample is then released, the tem- 1 perature is raised slowly, and the-sample is allowed to contract freely; The temperature at which the samplershows 10% 'of the total'r'etraction possible is the Tm'value. Thu"s,jthe lower the Tiovalue, the I greater is thefreezeresistance. I.

A series of fiuoroprene copolymers, "prepared and compoundedasdescribedabove, show the'fol- 9 lowing'properties 'after'vulcanization.

Tensile Per cent Percent Per cent 1 Per cent Tm 1 I 1 strength, elonga: kerosene. styrene I r rebound absorption 3,320 425 48 .-42-1o0.a 4,090 520 4:; 38 I am, 3,320 500 34 -29 92.0-

in the above table toillustrate'the improvement of tensile strength. obtained by copolymerization with styrene.

Copolymers of fiuoroprene'with '10 and of styrene, prepared, as described above, are

5 I compounded for electrical insulation purposes according to the following formula:

- The compounded -'-stocks are pressed into thin sheets and cured for minutes at 153 C. Thei electrical properties of the vulcanizates are'l11ustrated below. The properties of rubber, poly-1 chloroprene and a 90:IO'chIorQprene/styrene co-j i 5 ,These'vulcanizates show excellent resistance to swelling in water, showing 3% or.-less volume in- I crease after 2 days at 100 C; The tensile strength I 1 I of a similar vulcanizate ofpolyfluoroprene is given 85:

- I Parts I Polymer 100 Stearic c II I f 0.5 Phenyl-alpha-naphthylamine-r;;;; .i; 2.0

Blancfixefbarium sulfate) 100 catalpo clay 100 Semi-reinforcing carbon black 5 Litharge Y 20 polymer also compoundedby formulae .designed I to give good electrical properties, are included forg Electrical tests were determined'on specimens 6.x 6 x 0.02 0,inch. Dielectric constant and power factor tests were conducted at} frequencies of 1000 cycles per second. I I l It will be noted that in resistivity particularly the. "fluorop'rene/styrene vulcanizates are similar to -mers are much superior in oil'resistance' and in ozone or sunlightfresistance, showing at the same 1 time good freeze'resistance. Copolymerization of chloroprene with'10% of styrene leads to a product having improved resistivity but in contrast to thefluoroprene/styrene rubbers, such chloroprene --"-copolymersshow --no advantages over polychloroprene in tensile properties or in processing characteristics.;.. I

.It is to be understood that the examples are illustrativeon'ly, and-:that any ratio of monomers within the limits of 60% to 90% of fluoroprene and- ,40% -o,limpet styrene, .may be used. 7 At least ;10%..of'-':styrene is required to obtain the desired .,impr,ov ement in tensile properties and processing[characteristics in comparison with polyfluoroprene 'itself. In order to maintain a high degree of flexibilityand resilience, particularly at. low temperatures, not morev than 40% of styrehefis employed. I

It is. preferable in usingfiuoroprene prepared from mon'ovinylacetylene and hydrogen fluoride, that the monomer be essentially free of peroxides and :acetylenic compounds, although attractive copolymers from somewhatless pure fiuoroprene may be prepared by the properus ev of sulfur containing modifiers. Thus, if the-fiuoroprene contains an appreciable amountof monovinylacetylcnathe use of an increased proportion of long chain mercaptan in thepolymerization will tend to overcome the deleterious effect. of the acetylenic compounds upon the propertiesof the rubber. While the examples illustrate only the preparation ofimproved copolymers of 2-fluorobutadierie-Lii, it is to be understood that the invention isqapplicable likewise to polymerizable fluoroprene homologs such as 2-fluoro-3-methylbutadiene-1,3, 2-fiuoro-3-ethylbutadiene-1,3, or

2-fluoro-3-propylbutadiene-1,3.

The monomer mixture may be polymerized in' a any convenientmanner, but-generally best rej sultsare obtainedby using the emulsion polymerization technique. Although the alkaline sodium oleate system as described in the examplesis generally preferred, it is possible to use other emulsifying agents in either alkaline or acid mediawith equally good results.- Combinations of emulsifying agents "such as the alkali salts of'oleic acid and-rosin may also be employed to advantage. As polymerization catalyst,

potassium persulfate'is preferred, although other 'materials such as hydrogen peroxide, benzoyl peroxide, or sodium perborate may be used if desired. Catalyst activators such as potassium ferricyanide or sodium hydrosulfitausedin.con- I junction'with persulfates or peroxides, are especially beneficial by way of accelerating-polymerizations. As polymerization modifier, a long chain mercaptan such as voctyl, decyl, or 'lauryl mercaptan is preferably employed, but other known polymerization modifiers such as'sulfur,

dialkyl xanthogen disulfides, or carbon tetrachloride may be used. It is possible to carry out these polymerizations under. many diverse, conditions and in the presence of many different ingredients commonly used for the modification of haloprene or butadiene hydrocarbon polymerization systems.

The polymerization temperature may be varied I within the limits of 0 to C., temperatures of from 10 to 40 C. being preferred. 7 The time required to obtain high yields of polymerizate will vary,'of course, with the temperature, the catalyst, and the emulsion system employed.

The polymerized latex maybe stabilized in any suitable manner, but the addition of a dispersion of an aromatic amine such as phenyl-alphanaphthylamine, is preferred. It isalso possible to add the stabilizer to the coagulum on a rubber mill.

sulfate, or by freezing as describ'ed'in U. S. P.

The latex may be coagulated' by .alcohoL fl acids and brine or othersalts such as aluminum 2,187,146. The use of brine and anacid such as acetic or sulfuric acid is preferred forthe coagulation of sodium oleate latices. Processingof the coagulum can be carried out by conventional means. V The polymerization product prepared as described above may be compounded in many different ways in order to obtain vulcanizates having diflerent properties desired for specific uses. In general, the well-known techniques of compounding rubber and butadienecopolymer rubbers with sulfur, a vulcanization accelerator, and

a metallic oxide, are applicable to these products. The compounded mass may'the'n bejmolded, sheeted. calendered,- extruded or, in gen:ral, formed to the desired shape and vulcanized- The vulcanization may be carried out at room temperature or above','but preferably between 130? C. and 200 C. 1

The products of this invention are especially valuable for applications in which rubber-like materials are required having 'good electrical resistance combined with one or more of thefollowing properties, including high sunlight, ozone,

and oil resistance or good flexibility at low temperature. Specific applications requiring one'or more of these properties are encountered, for example, in the ignition and lighting systems of sisting of 2-fiuoro-1,3-butadiene and its methyl, 1 ethyl and propyl'homologs, and'styrene, in which r the styrene comprises from 10% to 40% of the tiles, for fabric coating by dipping or calendering, etc. i I

I claimi 1. A synthetic rubber-like material being a:

copolymer of a fluorobutadiene'of the class concopolymer, and the fluorobuta'diene the remainder.

2. A synthetic rubber-likematerial beinga co polymer of-2--fiuoro-1,3,-butadienev and styrene, in which'the styrene comprises from 10% to 40% of'the copolymers, and the 2-fiuoro-1,3-butadiene a the remainder.

3. A synthetic rubber-like material being acopolymer ofZ-fiuorq-lB-butadiene and styrene,.in

which the styrene comprises 10% of the co-- polymer, and the 2-fluoro-1,3-'butadiene the remainder.

fREFERE oEs CITED v The following references are of record in the file ofvthis patent: I

" STATES-PATENTS Number Name Date a 1 1,950,431 I Carothers Mar.,13, 1934 2,066,330 Carothers Jan. 5,1937" LEROY FRANK S ALISBURY v Meisenburg June 15,1943 

